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We study the rich globular cluster (GC) system in the center of the massivecluster of galaxies Abell 1689 (z=0.18), one of the most powerful gravitationallenses known. With 28 HST/ACS orbits in the F814W bandpass, we reach magnitudeI_814=29 with >90% completeness and sample the brightest ~5% of the GC system.Assuming the well-known Gaussian form of the GC luminosity function (GCLF), weestimate a total population of N(GC_total) = 162,850 GCs within a projectedradius of 400kpc. As many as half may comprise an intracluster component. Evenwith the sizable uncertainties, which mainly result from the uncertain GCLFparameters, this is by far the largest GC system studied to date. The specificfrequency S_N is high, but not uncommon for central galaxies in massiveclusters, rising from S_N~5 near the center to ~12 at large radii. Passivegalaxy fading would increase S_N by ~20% at z=0. We construct the radial massprofiles of the GCs, stars, intracluster gas, and lensing-derived total mass,and we compare the mass fractions as a function of radius. The estimated massin GCs, M(GC_total)=3.9x10^10 Msun, is comparable to ~80% of the total stellarmass of the Milky Way. The shape of the GC mass profile appears intermediatebetween those of the stellar light and total cluster mass. Despite the extremenature of this system, the ratios of the GC mass to the baryonic and totalmasses, and thus the GC formation efficiency, are typical of those in otherrich clusters when comparing at the same physical radii. The GC formationefficiency is not constant, but varies with radius, in a manner that appearssimilar for different clusters; we speculate on the reasons for this similarityin profile.

The Rich Globular Cluster System of Abell 1689 and the Radial Dependence of the Globular Cluster Formation Efficiency